Coal gasification process

Abstract

Low sulfur, iron and calcium containing solid carbonaceous fuel having a high melting point ash is mixed with a sufficient amount of iron sulfide containing material or supplemental iron and sulfur containing reactant materials that react in the reaction zone to produce iron and sulfur containing compounds. The mixture of materials is reacted in a free-flow gasifier by partial oxidation to produce a raw gas stream of synthesis gas, reducing gas or fuel gas, containing entrained particulate matter including molten slag. By the process, sufficient iron and sulfur are in the reaction zone so that the melting point of the fuel ash is decreased, and the mole ratio H 2 S/H 2 +CO in the raw gas stream is greater than 0.01. Further, the amount of iron in the molten ash is greater than 10.0 wt. %, and preferably at least 14 wt. % of the molten ash. By this means, the fluid temperature of the molten ash entrained in the raw gas stream is reduced at least 100° F. less than the fluid temperature of the fuel ash without the addition of iron and sulfur, and the gasifier may be operated in the molten slagging mode at a lower temperature. Further, coal wash tailings containing iron sulfides may be disposed of as a portion of the feed to the gasifier in an environmentally acceptable manner; and useful by-product sulfur may be recovered.

We claim: 
     
       1. A partial oxidation process comprising: (1) mixing together an ash-containing solid carbonaceous fuel containing less than about 2.0 wt. % sulfur, and in the noncombustible portion of said solid carbonaceous fuel less than 10 wt. % iron and less than about 8.0 wt. % of calcium with a sufficient amount of an ash-combining agent comprising iron sulfide containing material or supplemental iron containing reactant materials and sulfur containing reactant materials that react in the reaction zone in (2) to produce iron containing compounds and sulfur containing compounds that combine with the fuel ash; (2) reacting said mixture of materials optionally suspended in a liquid or gaseous medium by partial oxidation with a free-oxygen containing gas in the presence of H 2  O in a free-flow reaction zone in a reducing atmosphere at a temperature greater than about 2000° F. and below the fluid temperature of the ash in the solid carbonaceous fuel feed to the reaction zone and high enough to keep the ash produced in the molten state, and a pressure in the range of about 1 to 200 atmospheres, wherein the weight ratio of H 2  O to the solid carbonaceous fuel is in the range of about 0.33 to 1.0, to produce a raw effluent gas stream which is discharged downward through a bottom outlet in the reaction zone and which substantially comprises H 2 , CO, CO 2 , H 2  O, H 2  S, COS, entrained particulate matter including molten ash containing iron compounds whose iron content is greater than 10 wt. % of the molten ash, and optionally at least one material from the group CH 4 , N 2 , Ar, and NH 3  ; wherein sufficient iron and sulfur are in the reaction zone so that the melting point of the solid carbonaceous fuel ash is decreased and the fluid temperature of the molten ash entrained in the raw gas stream is reduced about 100° F. or more below the fluid temperature of the ash in the solid carbonaceous fuel without the addition of said ash-combining agent; excess H 2  S is present in the reaction zone and no free iron remains, and the mole ratio H 2  S/H 2  +CO in the raw gas stream is greater than 0.01; and (3) separating at least a portion of said particulate matter and molten ash from the raw gas stream. 
     
     
       2. The process of claim 1 wherein the iron content of the molten ash produced in step (2) is at least equivalent to 14.0 wt. % of the molten ash. 
     
     
       3. The process of claim 1 wherein prior, during, or subsequent to being mixed with said iron sulfide containing material or supplemental iron and sulfur containing reactant materials that react in the reaction zone in step (2) to produce iron and sulfur containing compounds, said solid carbonaceous fuel is ground so that at least 85 wt. % has a particle size of about 420 microns or smaller. 
     
     
       4. The process of claim 1 provided with the step of separating said H 2  S and COS from the raw gas stream in a gas purification zone. 
     
     
       5. The process of claim 4 provided with the step of recycling at least a portion of said separated H 2  S and COS back to step (1) as at least a portion of said sulfur containing reactant material. 
     
     
       6. The process of claim 4 provided with the step of processing said separated H 2  S and COS in a Claus unit to produce elemental sulfur. 
     
     
       7. The process of claim 1 wherein said iron sulfide containing material is selected from the group consisting of iron sulfide, coal cleaning waste products containing iron sulfide, and mixtures thereof. 
     
     
       8. The process of claim 1 wherein said iron containing reactant materials are selected from the group consisting of iron, iron oxide, iron carbonate, iron silicate, and mixtures thereof. 
     
     
       9. The process of claim 1 wherein said iron containing reactant materials are provided as an aqueous solution. 
     
     
       10. The process of claim 1 wherein said iron containing reactant materials are provided as a water soluble compound selected from the group consisting of ferrous sulfate, iron chloride, ferric nitrate, iron naphthenate, iron cyanides, and mixtures thereof. 
     
     
       11. The process of claim 1 wherein said sulfur containing reactant materials are selected from the group consisting of free sulfur, H 2  S, SO 2 , SO 3 , sulfuric acid, high sulfur containing carbonaceous feedstock, sulfuric acid recovery process sludge, sulfonation sludge, and mixtures thereof. 
     
     
       12. The process of claim 1 wherein said solid carbonaceous fuel is selected from the group consisting of coals including anthracite, bituminous, sub-bituminous, lignite; coke from coal; petroleum coke; soot; tar sand; asphalt; pitch; and mixtures thereof. 
     
     
       13. The process of claim 1 wherein the partial oxidation reaction in (2) takes place in the presence of a supplemental temperature moderator. 
     
     
       14. The process of claim 13 wherein a supplemental temperature moderator is selected from the group consisting of steam, water, CO 2  -rich gas, a portion of the cooled exhaust from a turbine employed downstream in the process, nitrogen, cooled synthesis gas and mixtures thereof. 
     
     
       15. The process of claim 1 wherein said mixture of materials in (1) is suspended in a liquid medium selected from the group consisting of a substantially thermally liquefiable or vaporizable hydrocarbon, water, and mixtures thereof. 
     
     
       16. The process of claim 1 wherein said mixture of materials in (1) is suspended in a gaseous medium selected from the group consisting of steam, CO 2 , N 2 , recycle stream of partially cooled raw effluent gas from the reaction zone, fuel gas, and mixtures thereof. 
     
     
       17. The process of claim 1 wherein said mixture of materials in (1) is introduced into the reaction zone in (2) as a pumpable slurry having a solids content in the range of about 50 to 75 wt. %. 
     
     
       18. The process of claim 17 wherein said slurry comprises said mixture of materials dispersed in a liquid slurrying medium selected from the group consisting of water, liquid hydrocarbon fuel, and mixtures thereof. 
     
     
       19. The process of claim 17 wherein said slurry includes dispersing and/or wetting agents.